Beta adrenergic blockade with propranolol can relieve angina pectoris, and may improve survival in some patients with cornary artery disease. Because it reduces contractility, it may cause clinically important left ventricular dysfunction in some patients with coronary artery disease. Therefore propranolol is often withheld if evidence of left ventricular dysfunction exists in the absence of drug. However, it is possible that by reducing myocardial oxygen demand in such patients, propranolol might actually prevent ischemic dysfunction, which otherwise might occur during stress. We tested the efficacy of propranolol in this setting with the use of non-invasive radionuclide cineangiography, and determined that the drug causes mild depression of function in non-ischemic regions of the left ventricle during exercise, and spares the function of ischemic regions during exercise.